package org.apache.solr.search.grouping;

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.search.Collector;
import org.apache.lucene.search.Sort;
import org.apache.solr.schema.SchemaField;

import java.io.IOException;
import java.util.List;

/**
 * Defines a grouping command. This is an abstraction on how the
 * {@link Collector} instances are created and how the results are retrieved
 * from the {@link Collector} instances.
 * 
 * @lucene.experimental
 */
public interface Command<T> {

	/**
	 * Returns a list of {@link Collector} instances to be included in the
	 * search based on the .
	 * 
	 * @return a list of {@link Collector} instances
	 * @throws IOException
	 *             If I/O related errors occur
	 */
	List<Collector> create() throws IOException;

	/**
	 * Returns the results that the collectors created by {@link #create()}
	 * contain after a search has been executed.
	 * 
	 * @return The results of the collectors
	 */
	T result();

	/**
	 * @return The key of this command to uniquely identify itself
	 */
	String getKey();

	/**
	 * @return The group sort (overall sort)
	 */
	Sort getGroupSort();

	/**
	 * @return The sort inside a group
	 */
	Sort getSortWithinGroup();

}
